A current transformer of the above-mentioned type has been disclosed, for example, in U.S. Pat. No. 3,380,809. In the known current transformers of this type, the entire space inside a hollow procelain insulator is in communication with the interior of a top housing for the primary conductor and the coils of the secondary circuit. As a result, the pressure of the insulating gas, which separates the secondary coils and a lead-through tube for the secondary circuit terminal leads from the primary conductor and from the top housing, which also carries a high voltage, acts also on the procelain insulator. Due to its comparatively low mechanical strength, the insulator constitutes the limiting factor for the permissible gas pressure. In order to increase the permissible gas pressure, and hence the dielectric strength of the gas and the voltage which can be applied to the current transformers of the aforementioned type, the top housing and the procelain insulator are braced. However, apart from achieving only a slight increase in the permissible gas pressure, this approach is susceptible to problems arising from the dissimilar thermal expansion exhibited by the insulator and the lead through.